Wooden structural members are used increasingly in a number of building applications. This can be seen, for example, in the use of wooden I-beams to replace conventional solid wood 2.times.8, 2.times.10 and other size lumber in the supporting structure for floors, roofs and the like. Such structural members can be of substantially greater stiffness than conventional lumber elements and can thus be used over greater spans. Advantages are thus offered for example, in the elimination of supporting division walls and of foundation work below such walls.
As well, old growth large diameter softwoods are gradually disappearing, and consequently suitable long and wide solid wood joists and beams are becoming scarcer and more costly.
There are thus ongoing attempts to develop wooden structural members using in part composite panels and offering advantages in ease of manufacture and reliability.
The structural members under discussion here will comprise flange members which include aligned grooves in opposed surfaces. One or more web members will be positioned between the opposed faces of the flanges with the edges of the web inserted into the grooves.
The primary difficulty in constructing these wooden structural members has been in achieving a good joint between the web and the flanges.
Several types of problems arise in attempting to manufacture wooden I-beams. These relate to the manufacturing process itself, to the glue line achieved during manufacturing and to the problem of swelling due to uptake of moisture which is inherent in the materials used.
The manufacturing problems arise primarily out of the need to manufacture at high speed in order to have an economically viable product. For example, it may well be the case that the use of a jig to hold the components of the member in position during the setting of the glue, which subsequently holds the components together, would in itself eliminate economic viability. Thus, the flange to web joint must be one which can achieve an acceptable glue line without the use of such jigs.
A further manufacturing problem is the rather basic one that the components must be able to be fitted together quickly without irregular or unexpected disruptions during assembly. For example, the edge of the web must move smoothly into the mouth of the groove without interference at the outside edges of the groove.
Problems involved in establishing an acceptable glue line are related to the above manufacturing problems. For example, the web must be readily insertable into the groove in the flange but at the same time, once inserted, must provide good continuous pressure at all points between the interior surfaces of the groove and the exterior surfaces of the inserted part of the web. Furthermore, such a glue line requires good distribution of glue within the joint. Distribution of glue can be seriously impaired if, as discussed above, the edge of the web scrapes along the sides of the groove, scraping glue off the sides as it progresses into the groove.
Both the manufacturing and the glue line problems are related to a third inherent problem which is always present in working with wood. This third problem relates to swelling or shrinkage of wood arising from the changing moisture content of the wood and the changing stresses within the wood. Thus, for example, when a groove is produced in a piece of solid lumber, the release of stress in the wood can cause the groove to open substantially in a short period of time. Similarly, a change in moisture content of the various wooden components can dramatically affect the size of the wood, as, for example, the thickness of the web. It is therefore essential that the joint take into account this problem, since catastrophic failure of the flange may otherwise result.
To date no joint is available which addresses in an adequate way and reconciles differences between all these various types of problems.
Against this background the present invention provides a structural member having an improved web to flange joint.